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<!--========================================================================-->
<H1>Title</H1>

<div class=title-text>SRFI 14: Character-set Library</div>

<!--========================================================================-->
<H1>Author</H1>

Olin Shivers

<H1>Status</H1>
This SRFI is currently in ``final'' status.  To see an explanation of each status that a SRFI can hold, see <A HREF="http://srfi.schemers.org/srfi-process.html">here</A>.
You can access the discussion via <A HREF="http://srfi.schemers.org/srfi-14/mail-archive/maillist.html">the archive of the mailing list</A>.
<P><UL>
<LI>Received: 1999/10/17
<LI>Draft: 1999/10/30-1999/12/30
<LI>Revised: 2000/04/30
<LI>Revised: 2000/04/30
<LI>Revised: 2000/06/09
<LI>Revised: 2000/12/23
</UL>

<!--========================================================================-->
<h1>Table of contents</H1>

<!-- A bug in netscape (?) keeps the first link in this UL from being active.
==== So the Abstract link be dead. 99/8/22 -Olin
-->
<ul id=toc-table>
<li><a href="#Abstract">Abstract</a>
<li><a href="#VariableIndex">Variable index</a>
<li><a href="#Rationale">Rationale</a>
  <ul>
  <li><a href="#LinearUpdateOperations">"Linear-update" operations</a>
  <li><a href="#ExtraSRFI">Extra-SRFI recommendations</a>
  </ul>

<li><a href="#Specification">Specification</a>
  <ul>
  <li><a href="#GeneralProcs">General procedures</a>
  <li><a href="#Iterating">Iterating over character sets</a>
  <li><a href="#Creating">Creating character sets</a>
  <li><a href="#Querying">Querying character sets</a>
  <li><a href="#Algebra">Character set algebra</a>
  <li><a href="#StandardCharsets">Standard character sets</a>
  </ul>

<li><a href="#StandardCharsetDefs">Unicode, Latin-1 and ASCII definitions of the standard character sets</a>
<li><a href="#ReferenceImp">Reference implementation</a>
<li><a href="#Acknowledgements">Acknowledgements</a>
<li><a href="#Links">References &amp; Links</a>
<li><a href="#Copyright">Copyright</a>
</ul>

<!--========================================================================-->
<h1><a name="Abstract">Abstract</a></H1>
<p>

The ability to efficiently represent and manipulate sets of characters is an
unglamorous but very useful capability for text-processing code -- one that
tends to pop up in the definitions of other libraries.  Hence it is useful to
specify a general substrate for this functionality early.  This SRFI defines a
general library that provides this functionality. 

It is accompanied by a reference implementation for the spec. The reference
implementation is fairly efficient, straightforwardly portable, and has a
"free software" copyright. The implementation is tuned for "small" 7 or 8
bit character types, such as ASCII or Latin-1; the data structures and
algorithms would have to be altered for larger 16 or 32 bit character types
such as Unicode -- however, the specs have been carefully designed with these
larger character types in mind.

Several forthcoming SRFIs can be defined in terms of this one:
<ul>
    <li> string library
    <li> delimited input procedures (<em>e.g.</em>, <code>read-line</code>)
    <li> regular expressions
</ul>


<!--========================================================================-->
<h1><a name="VariableIndex">Variable Index</a></h1>
<p>
Here is the complete set of bindings -- procedural and otherwise --
exported by this library. In a Scheme system that has a module or package 
system, these procedures should be contained in a module named "char-set-lib".

<div class=indent>
<dl>
<dt class=proc-index> Predicates &amp; comparison
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set-p">char-set?</a> <a href="#char-set=">char-set=</a> <a href="#char-set<=">char-set<=</a> <a href="#char-set-hash">char-set-hash</a>
</pre>

<dt class=proc-index> Iterating over character sets
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set-cursor">char-set-cursor</a> <a href="#char-set-ref">char-set-ref</a> <a href="#char-set-cursor-next">char-set-cursor-next</a> <a href="#end-of-char-set-p">end-of-char-set?</a> 
<a href="#char-set-fold">char-set-fold</a> <a href="#char-set-unfold">char-set-unfold</a> <a href="#char-set-unfold!">char-set-unfold!</a>
<a href="#char-set-for-each">char-set-for-each</a> <a href="#char-set-map">char-set-map</a>
</pre>

<dt class=proc-index> Creating character sets
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set-copy">char-set-copy</a> <a href="#char-set">char-set</a>

<a href="#list->char-set">list->char-set</a>  <a href="#string->char-set">string->char-set</a>
<a href="#list->char-set!">list->char-set!</a> <a href="#string->char-set!">string->char-set!</a>
    
<a href="#char-set-filter">char-set-filter</a>  <a href="#ucs-range->char-set">ucs-range->char-set</a> <a href="#
char-set-filter!">
char-set-filter!</a> <a href="#ucs-range->char-set!">ucs-range->char-set!</a>

<a href="#->char-set">->char-set</a>
</pre>

<dt class=proc-index> Querying character sets
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set->list">char-set->list</a> <a href="#char-set->string">char-set->string</a>
<a href="#char-set-size">char-set-size</a> <a href="#char-set-count">char-set-count</a> <a href="#char-set-contains-p">char-set-contains?</a>
<a href="#char-set-every">char-set-every</a> <a href="#char-set-any">char-set-any</a>
</pre>

<dt class=proc-index> Character-set algebra
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set-adjoin">char-set-adjoin</a>  <a href="#char-set-delete">char-set-delete</a>
<a href="#char-set-adjoin!">char-set-adjoin!</a> <a href="#char-set-delete!">char-set-delete!</a>

<a href="#char-set-complement">char-set-complement</a>  <a href="#char-set-union">char-set-union</a>  <a href="#char-set-intersection">char-set-intersection</a>
<a href="#char-set-complement!">char-set-complement!</a> <a href="#char-set-union!">char-set-union!</a> <a href="#char-set-intersection!">char-set-intersection!</a>

<a href="#char-set-difference">char-set-difference</a>  <a href="#char-set-xor">char-set-xor</a>  <a href="#char-set-diff+intersection">char-set-diff+intersection</a>
<a href="#char-set-difference!">char-set-difference!</a> <a href="#char-set-xor!">char-set-xor!</a> <a href="#char-set-diff+intersection!">char-set-diff+intersection!</a>
</pre>

<dt class=proc-index> Standard character sets
<dd class=proc-index>
<pre class=proc-index>
<a href="#char-set:lower-case">char-set:lower-case</a>  <a href="#char-set:upper-case">char-set:upper-case</a>  <a href="#char-set:title-case">char-set:title-case</a>
<a href="#char-set:letter">char-set:letter</a>      <a href="#char-set:digit">char-set:digit</a>       <a href="#char-set:letter+digit">char-set:letter+digit</a>
<a href="#char-set:graphic">char-set:graphic</a>     <a href="#char-set:printing">char-set:printing</a>    <a href="#char-set:whitespace">char-set:whitespace</a>
<a href="#char-set:iso-control">char-set:iso-control</a> <a href="#char-set:punctuation">char-set:punctuation</a> <a href="#char-set:symbol">char-set:symbol</a>
<a href="#char-set:hex-digit">char-set:hex-digit</a>   <a href="#char-set:blank">char-set:blank</a>       <a href="#char-set:ascii">char-set:ascii</a>
<a href="#char-set:empty">char-set:empty</a>       <a href="#char-set:full">char-set:full</a>
</pre>

</dl>
</div>

<!--========================================================================-->
<h1><a name="Rationale">Rationale</a></h1>

<p>
The ability to efficiently manipulate sets of characters is quite
useful for text-processing code. Encapsulating this functionality in
a general, efficiently implemented library can assist all such code.
This library defines a new data structure to represent these sets, called
a "char-set." The char-set type is distinct from all other types.

<p>
This library is designed to be portable across implementations that use
different character types and representations, especially ASCII, Latin-1
and Unicode. Some effort has been made to preserve compatibility with Java
in the Unicode case (see the definition of <code>char-set:whitespace</code> for the
single real deviation).

<!--========================================================================-->
<h2><a name="LinearUpdateOperations">Linear-update operations</a></h2>

<p>
The procedures of this SRFI, by default, are "pure functional" -- they do not
alter their parameters. However, this SRFI defines a set of "linear-update"
procedures which have a hybrid pure-functional/side-effecting semantics: they
are allowed, but not required, to side-effect one of their parameters in order
to construct their result. An implementation may legally implement these
procedures as pure, side-effect-free functions, or it may implement them using
side effects, depending upon the details of what is the most efficient or
simple to implement in terms of the underlying representation.

<p>
The linear-update routines all have names ending with "!".

<p>
Clients of these procedures <em>may not</em> rely upon these procedures working by
side effect. For example, this is not guaranteed to work:
<pre class=code-example>
(let* ((cs1 (char-set #\a #\b #\c))      ; cs1 = {a,b,c}.
       (cs2 (char-set-adjoin! cs1 #\d))) ; Add d to {a,b,c}.
  cs1) ; Could be either {a,b,c} or {a,b,c,d}.
</pre>
<p class=continue>
However, this is well-defined:
<pre class=code-example>
(let ((cs (char-set #\a #\b #\c)))
  (char-set-adjoin! cs #\d)) ; Add d to {a,b,c}.
</pre>

<p>
So clients of these procedures write in a functional style, but must
additionally be sure that, when the procedure is called, there are no other
live pointers to the potentially-modified character set (hence the term
"linear update").

<p>
There are two benefits to this convention:
<ul>
  <li> Implementations are free to provide the most efficient possible
    implementation, either functional or side-effecting.
  <li> Programmers may nonetheless continue to assume that character sets
    are purely functional data structures: they may be reliably shared
    without needing to be copied, uniquified, and so forth.
</ul>

<p>
Note that pure functional representations are the right thing for
ASCII- or Latin-1-based Scheme implementations, since a char-set can
be represented in an ASCII Scheme with 4 32-bit words. Pure set-algebra
operations on such a representation are very fast and efficient. Programmers
who code using linear-update operations are guaranteed the system will
provide the best implementation across multiple platforms.

<p>
In practice, these procedures are most useful for efficiently constructing
character sets in a side-effecting manner, in some limited local context, 
before passing the character set outside the local construction scope to be
used in a functional manner.

<p>
Scheme provides no assistance in checking the linearity of the potentially
side-effected parameters passed to these functions --- there's no linear
type checker or run-time mechanism for detecting violations. (But
sophisticated programming environments, such as DrScheme, might help.)

<!--========================================================================-->
<h2><a name="ExtraSRFI">Extra-SRFI recommendations</a></h2>
<p>
Users are cautioned that the R5RS predicates 
<div class=inset><code>
char-alphabetic? <br>
char-numeric? <br>
char-whitespace? <br>
char-upper-case? <br>
char-lower-case? <br>
</code>
</div>
<p class=continue>
may or may not be in agreement with the SRFI 14 base character sets
<div class=inset>
<code>
char-set:letter<br>
char-set:digit<br>
char-set:whitespace<br>
char-set:upper-case<br>
char-set:lower-case<br>
</code>
</div>
<p class=continue>
Implementors are strongly encouraged to bring these predicates into
agreement with the base character sets of this SRFI; not to do so risks
major confusion.


<!--========================================================================-->
<h1><a name="Specification">Specification</a></h1>
<p>
In the following procedure specifications:
<ul>
    <li> A <var>cs</var> parameter is a character set.

    <li> An <var>s</var> parameter is a string.

    <li> A <var>char</var> parameter is a character.

    <li> A <var>char-list</var> parameter is a list of characters.

    <li> A <var>pred</var> parameter is a unary character predicate procedure, returning 
      a true/false value when applied to a character.

    <li> An <var>obj</var> parameter may be any value at all.
</ul>

<p>
Passing values to procedures with these parameters that do not satisfy these
types is an error.

<p>
Unless otherwise noted in the specification of a procedure, procedures
always return character sets that are distinct (from the point of view
of the linear-update operations) from the parameter character sets. For
example, <code>char-set-adjoin</code> is guaranteed to provide a fresh character set,
even if it is not given any character parameters.

<p>
Parameters given in square brackets are optional. Unless otherwise noted in the
text describing the procedure, any prefix of these optional parameters may
be supplied, from zero arguments to the full list. When a procedure returns
multiple values, this is shown by listing the return values in square
brackets, as well. So, for example, the procedure with signature
<pre class=code-example>
halts? <var>f [x init-store]</var> -> <var>[boolean integer]</var>
</pre>
would take one (<var>f</var>), two (<var>f</var>, <var>x</var>) 
or three (<var>f</var>, <var>x</var>, <var>init-store</var>) input parameters, 
and return two values, a boolean and an integer.

<p>
A parameter followed by "<code>...</code>" means zero-or-more elements. 
So the procedure with the signature
<pre class=code-example>
sum-squares <var>x ... </var> -> <var>number</var>
</pre>
takes zero or more arguments (<var>x ...</var>), 
while the procedure with signature
<pre class=code-example>
spell-check <var>doc dict<sub>1</sub> dict<sub>2</sub> ...</var> -> <var>string-list</var>
</pre>
takes two required parameters 
(<var>doc</var> and <var>dict<sub>1</sub></var>) 
and zero or more optional parameters (<var>dict<sub>2</sub> ...</var>).


<!--========================================================================-->
<h2><a name="GeneralProcs">General procedures</a></h2>
<dl>

<!--
==== char-set?
============================================================================-->
<dt class=proc-def>
<a name="char-set-p"></a>
<code class=proc-def>char-set?</code><var> obj -> boolean</var>
<dd class=proc-def>

    Is the object <var>obj</var> a character set?

<!--
==== char-set=
============================================================================-->
<dt class=proc-def>
<a name="char-set="></a>
<code class=proc-def>char-set=</code><var> cs<sub>1</sub> ... -> boolean</var>
<dd class=proc-def>
    Are the character sets equal?
<p>
    Boundary cases:
<pre class=code-example>
(char-set=) => <var>true</var>
(char-set= cs) => <var>true</var>
</pre>

<p>
    Rationale: transitive binary relations are generally extended to n-ary
    relations in Scheme, which enables clearer, more concise code to be
    written. While the zero-argument and one-argument cases will almost
    certainly not arise in first-order uses of such relations, they may well
    arise in higher-order cases or macro-generated code. 
    <em>E.g.,</em> consider
<pre class=code-example>
(apply char-set= cset-list)
</pre>
<p class=continue>
    This is well-defined if the list is empty or a singleton list. Hence
    we extend these relations to any number of arguments. Implementors
    have reported actual uses of n-ary relations in higher-order cases
    allowing for fewer than two arguments. The way of Scheme is to handle the
    general case; we provide the fully general extension.
<p>
    A counter-argument to this extension is that 
    <abbr title="Revised^5 Report on Scheme"><a href="#R5RS">R5RS</a></abbr>'s
    transitive binary arithmetic relations 
    (<code>=</code>, <code>&lt;</code>, <em>etc.</em>) 
    require at least two arguments, hence
    this decision is a break with the prior convention -- although it is
    at least one that is backwards-compatible.

<!--
==== char-set<=
============================================================================-->
<dt class=proc-def>
<a name="char-set<="></a>
<code class=proc-def>char-set<=</code><var> cs<sub>1</sub> ... -> boolean</var>
<dd class=proc-def>
    Returns true if every character set <var>cs<sub>i</sub></var> is 
    a subset of character set <var>cs<sub>i+1</sub></var>.

<p>
Boundary cases:
<pre class=code-example>
(char-set<=) => <var>true</var>
(char-set<= cs) => <var>true</var>
</pre>
<p>
Rationale: See <code>char-set=</code> for discussion of zero- and one-argument
applications. Consider testing a list of char-sets for monotonicity
with 
<pre class=code-example>
(apply char-set<= cset-list)
</pre>

<!--
==== char-set-hash
============================================================================-->
<dt class=proc-def>
<a name="char-set-hash"></a>
<code class=proc-def>char-set-hash</code><var> cs [bound] -> integer</var>
<dd class=proc-def>
    Compute a hash value for the character set <var>cs</var>. 
    <var>Bound</var> is a non-negative
    exact integer specifying the range of the hash function. A positive
    value restricts the return value to the range [0,<var>bound</var>).

    <p>
    If <var>bound</var> is either zero or not given, the implementation may use
    an implementation-specific default value, chosen to be as large as
    is efficiently practical. For instance, the default range might be chosen
    for a given implementation to map all strings into the range of
    integers that can be represented with a single machine word.


    <p>
    Invariant:
<pre class=code-example>
(char-set= cs<sub>1</sub> cs<sub>2</sub>) => (= (char-set-hash cs<sub>1</sub> b) (char-set-hash cs<sub>2</sub> b))
</pre>

    <p>
    A legal but nonetheless discouraged implementation:
<pre class=code-example>
(define (char-set-hash cs . maybe-bound) 1)
</pre>

<p>
    Rationale: allowing the user to specify an explicit bound simplifies user
    code by removing the mod operation that typically accompanies every hash
    computation, and also may allow the implementation of the hash function to
    exploit a reduced range to efficiently compute the hash value. 
    <em>E.g.</em>, for
    small bounds, the hash function may be computed in a fashion such that
    intermediate values never overflow into bignum integers, allowing the
    implementor to provide a fixnum-specific "fast path" for computing the
    common cases very rapidly.

</dl>

<!--========================================================================-->
<h2><a name="Iterating">Iterating over character sets</a></h2>

<dl>
<!--
==== char-set-cursor char-set-ref char-set-cursor-next end-of-char-set?
============================================================================-->
<dt class=proc-def1>
<a name="char-set-cursor"></a>
<a name="char-set-ref"></a>
<a name="char-set-cursor-next"></a>
<a name="end-of-char-set-p"></a>
<code class=proc-def>char-set-cursor</code><var> cset -> cursor</var>
<dt class=proc-defi>
<code class=proc-def>char-set-ref</code><var> cset cursor -> char</var>
<dt class=proc-defi>
<code class=proc-def>char-set-cursor-next</code><var> cset cursor -> cursor</var>
<dt class=proc-defn>
<code class=proc-def>end-of-char-set?</code><var> cursor -> boolean</var>
<dd class=proc-def>
    Cursors are a low-level facility for iterating over the characters in a
    set. A cursor is a value that indexes a character in a char set.
    <code>char-set-cursor</code> produces a new cursor for a given char set. 
    The set element indexed by the cursor is fetched with 
    <code>char-set-ref</code>. 
    A cursor index is incremented with <code>char-set-cursor-next</code>; 
    in this way, code can step through every character in a char set. 
    Stepping a cursor "past the end" of a char set produces a cursor that 
    answers true to <code>end-of-char-set?</code>. 
    It is an error to pass such a cursor to <code>char-set-ref</code> or to
    <code>char-set-cursor-next</code>.

<p>
    A cursor value may not be used in conjunction with a different character
    set; if it is passed to <code>char-set-ref</code> or 
    <code>char-set-cursor-next</code> with
    a character set other than the one used to create it, the results and
    effects are undefined.

<p>
    Cursor values are <em>not</em> necessarily distinct from other types. 
    They may be
    integers, linked lists, records, procedures or other values. This license
    is granted to allow cursors to be very "lightweight" values suitable for
    tight iteration, even in fairly simple implementations.

<p>
    Note that these primitives are necessary to export an iteration facility
    for char sets to loop macros.

<p>
    Example:
<pre class=code-example>
(define cs (char-set #\G #\a #\T #\e #\c #\h))

;; Collect elts of CS into a list.
(let lp ((cur (char-set-cursor cs)) (ans '()))
  (if (end-of-char-set? cur) ans
      (lp (char-set-cursor-next cs cur)
          (cons (char-set-ref cs cur) ans))))
  => (#\G #\T #\a #\c #\e #\h)

;; Equivalently, using a list unfold (from SRFI 1):
(unfold-right end-of-char-set? 
              (curry char-set-ref cs)
	      (curry char-set-cursor-next cs)
	      (char-set-cursor cs))
  => (#\G #\T #\a #\c #\e #\h)
</pre>

<p>
    Rationale: Note that the cursor API's four functions "fit" the functional
    protocol used by the unfolders provided by the list, string and char-set
    SRFIs (see the example above). By way of contrast, here is a simpler, 
    two-function API that was rejected for failing this criterion. Besides 
    <code>char-set-cursor</code>, it provided a single
    function that mapped a cursor and a character set to two values, the
    indexed character and the next cursor. If the cursor had exhausted the
    character set, then this function returned false instead of the character
    value, and another end-of-char-set cursor. In this way, the other three
    functions of the current API were combined together.

<!--
==== char-set-fold
============================================================================-->
<dt class=proc-def>
<a name="char-set-fold"></a>
<code class=proc-def>char-set-fold</code><var> kons knil cs -> object</var>
<dd class=proc-def>
    This is the fundamental iterator for character sets.  Applies the function
    <var>kons</var> across the character set <var>cs</var> using initial state value <var>knil</var>.  That is,
    if <var>cs</var> is the empty set, the procedure returns <var>knil</var>.  Otherwise, some
    element <var>c</var> of <var>cs</var> is chosen; 
    let <var>cs'</var> be the remaining, unchosen characters.
    The procedure returns
<pre class=code-example>
(char-set-fold <var>kons</var> (<var>kons</var> <var>c</var> <var>knil</var>) <var>cs'</var>)
</pre>
    <p>
    Examples:
<pre class=code-example>
;; CHAR-SET-MEMBERS
(lambda (cs) (char-set-fold cons '() cs))

;; CHAR-SET-SIZE
(lambda (cs) (char-set-fold (lambda (c i) (+ i 1)) 0 cs))

;; How many vowels in the char set?
(lambda (cs) 
  (char-set-fold (lambda (c i) (if (vowel? c) (+ i 1) i))
                 0 cs))
</pre>

<!--
==== char-set-unfold char-set-unfold!
============================================================================-->
<dt class=proc-def1>
<a name="char-set-unfold"></a>
<a name="char-set-unfold!"></a>
<code class=proc-def>char-set-unfold&nbsp;</code><var> f p g seed [base-cs] -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-unfold!</code><var> f p g seed base-cs -> char-set</var>
<dd class=proc-def>
    This is a fundamental constructor for char-sets. 
<ul>
    <li> <var>G</var> is used to generate a series of "seed" values from the initial seed:
        <var>seed</var>, (<var>g</var> <var>seed</var>), (<var>g<sup>2</sup></var> <var>seed</var>), (<var>g<sup>3</sup></var> <var>seed</var>), ...
    <li> <var>P</var> tells us when to stop -- when it returns true when applied to one 
      of these seed values.
    <li> <var>F</var> maps each seed value to a character. These characters are added
      to the base character set <var>base-cs</var> to form the result; <var>base-cs</var> defaults to
      the empty set. <code>char-set-unfold!</code> adds the characters to <var>base-cs</var> in a 
      linear-update -- it is allowed, but not required, to side-effect
      and use <var>base-cs</var>'s storage to construct the result.
</ul>

    <p>
    More precisely, the following definitions hold, ignoring the
    optional-argument issues:

<pre class=code-example>
(define (char-set-unfold p f g seed base-cs) 
  (char-set-unfold! p f g seed (char-set-copy base-cs)))

(define (char-set-unfold! p f g seed base-cs)
  (let lp ((seed seed) (cs base-cs))
        (if (p seed) cs                                 ; P says we are done.
            (lp (g seed)                                ; Loop on (G SEED).
                (char-set-adjoin! cs (f seed))))))      ; Add (F SEED) to set.
</pre>

    (Note that the actual implementation may be more efficient.)

    <p>
    Examples:
<pre class=code-example>                         
(port->char-set p) = (char-set-unfold eof-object? values
                                      (lambda (x) (read-char p))
                                      (read-char p))

(list->char-set lis) = (char-set-unfold null? car cdr lis)
</pre>
<!--
==== char-set-for-each
============================================================================-->
<dt class=proc-def>
<a name="char-set-for-each"></a>
<code class=proc-def>char-set-for-each</code><var> proc cs -> unspecified</var>
<dd class=proc-def>
    Apply procedure <var>proc</var> to each character in the character set <var>cs</var>.
    Note that the order in which <var>proc</var> is applied to the characters in the
    set is not specified, and may even change from one procedure application
    to another.

    <p>
    Nothing at all is specified about the value returned by this procedure; it
    is not even required to be consistent from call to call. It is simply
    required to be a value (or values) that may be passed to a command
    continuation, <em>e.g.</em> as the value of an expression appearing as a
    non-terminal subform of a <code>begin</code> expression. 
    Note that in 
    <abbr title="Revised^5 Report on Scheme"><a href="#R5RS">R5RS</a></abbr>,
    this restricts the procedure to returning a single value; 
    non-R5RS systems may not even provide this restriction.

<!--
==== char-set-map
============================================================================-->
<dt class=proc-def>
<a name="char-set-map"></a>
<code class=proc-def>char-set-map</code><var> proc cs -> char-set</var>
<dd class=proc-def>
    <var>proc</var> is a char->char procedure. Apply it to all the characters in
    the char-set <var>cs</var>, and collect the results into a new character set.

    <p>
    Essentially lifts <var>proc</var> from a char->char procedure to a char-set ->
    char-set procedure.

    <p>
    Example:
<pre class=code-example>
(char-set-map char-downcase cset)
</pre>
</dl>


<!--========================================================================-->
<h2><a name="Creating">Creating character sets</a></h2>
<dl>

<!--
==== char-set-copy
============================================================================-->
<dt class=proc-def>
<a name="char-set-copy"></a>
<code class=proc-def>char-set-copy</code><var> cs -> char-set</var>
<dd class=proc-def>
    Returns a copy of the character set <var>cs</var>.  "Copy" means that if either the
    input parameter or the result value of this procedure is passed to one of
    the linear-update procedures described below, the other character set is
    guaranteed not to be altered.  

    <p>
    A system that provides pure-functional implementations of the
    linear-operator suite could implement this procedure as the identity
    function -- so copies are <em>not</em> guaranteed to be distinct by <code>eq?</code>.

<!--
==== char-set
============================================================================-->
<dt class=proc-def>
<a name="char-set"></a>
<code class=proc-def>char-set</code><var> char<sub>1</sub> ... -> char-set</var>
<dd class=proc-def>
    Return a character set containing the given characters.

<!--
==== list->char-set list->char-set
============================================================================-->
<dt class=proc-def1>
<a name="list->char-set"></a>
<a name="list->char-set!"></a>
<code class=proc-def>list->char-set&nbsp;</code><var> char-list [base-cs] -> char-set</var>
<dt class=proc-defn><code class=proc-def>list->char-set!</code><var> char-list base-cs -> char-set</var>
<dd class=proc-def>
    Return a character set containing the characters in the list of
    characters <var>char-list</var>.

    <p>
    If character set <var>base-cs</var> is provided, the characters from <var>char-list</var>
    are added to it. <code>list->char-set!</code> is allowed, but not required,
    to side-effect and reuse the storage in <var>base-cs</var>; 
    <code>list->char-set</code> produces a fresh character set.

<!--
==== string->char-set string->char-set!
============================================================================-->
<dt class=proc-def1>
<a name="string->char-set"></a>
<a name="string->char-set!"></a>
<code class=proc-def>string->char-set&nbsp;</code><var> s [base-cs] -> char-set</var>
<dt class=proc-defn><code class=proc-def>string->char-set!</code><var> s base-cs -> char-set</var>
<dd class=proc-def>

    Return a character set containing the characters in the string <var>s</var>.

    <p>
    If character set <var>base-cs</var> is provided, the characters from <var>s</var> are added to
    it. <code>string->char-set!</code> is allowed, but not required, to side-effect and
    reuse the storage in <var>base-cs</var>; <code>string->char-set</code> produces a fresh character
    set.

<!--
==== char-set-filter char-set-filter!
============================================================================-->
<dt class=proc-def1>
<a name="char-set-filter"></a>
<a name="char-set-filter!"></a>
<code class=proc-def>char-set-filter&nbsp;</code><var> pred cs [base-cs] -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-filter!</code><var> pred cs base-cs -> char-set</var>
<dd class=proc-def>

    Returns a character set containing every character <var>c</var> 
    in <var>cs</var> such that <code>(<var>pred</var> <var>c</var>)</code> 
    returns true.

<p>
    If character set <var>base-cs</var> is provided, the characters specified 
    by <var>pred</var> are added to it. 
    <code>char-set-filter!</code> is allowed, but not required,
    to side-effect and reuse the storage in <var>base-cs</var>; 
    <code>char-set-filter</code> produces a fresh character set.

<p>
    An implementation may not save away a reference to <var>pred</var> and
    invoke it after <code>char-set-filter</code> or 
    <code>char-set-filter!</code> returns -- that is, "lazy,"
    on-demand implementations are not allowed, as <var>pred</var> may have
    external dependencies on mutable data or have other side-effects.

<p>
    Rationale: This procedure provides a means of converting a character
    predicate into its equivalent character set; the <var>cs</var> parameter
    allows the programmer to bound the predicate's domain. Programmers should
    be aware that filtering a character set such as <code>char-set:full</code>
    could be a very expensive operation in an implementation that provided an
    extremely large character type, such as 32-bit Unicode. An earlier draft
    of this library provided a simple <code>predicate->char-set</code>
    procedure, which was rejected in favor of <code>char-set-filter</code> for
    this reason.


<!--
==== ucs-range->char-set ucs-range->char-set!
============================================================================-->
<dt class=proc-def1>
<a name="ucs-range->char-set"></a>
<a name="ucs-range->char-set!"></a>
<code class=proc-def>ucs-range->char-set&nbsp;</code><var> lower upper [error? base-cs] -> char-set</var>
<dt class=proc-defn><code class=proc-def>ucs-range->char-set!</code><var> lower upper error? base-cs -> char-set</var>
<dd class=proc-def>
    <var>Lower</var> and <var>upper</var> are exact non-negative integers; 
    <var>lower</var> <= <var>upper</var>.

    <p>
    Returns a character set containing every character whose ISO/IEC 10646
    UCS-4 code lies in the half-open range [<var>lower</var>,<var>upper</var>).

<ul>
    <li> If the requested range includes unassigned UCS values, these are
      silently ignored (the current UCS specification has "holes" in the
      space of assigned codes).
    
    <li> If the requested range includes "private" or "user space" codes, these
      are handled in an implementation-specific manner; however, a UCS- or
      Unicode-based Scheme implementation should pass them through
      transparently.
    
    <li> If any code from the requested range specifies a valid, assigned
      UCS character that has no corresponding representative in the
      implementation's character type, then (1) an error is raised if <var>error?</var>
      is true, and (2) the code is ignored if <var>error?</var> is false (the default).
      This might happen, for example, if the implementation uses ASCII
      characters, and the requested range includes non-ASCII characters.
</ul>

    <p>
    If character set <var>base-cs</var> is provided, the characters specified by the
    range are added to it. <code>ucs-range->char-set!</code> is allowed, but not required,
    to side-effect and reuse the storage in <var>base-cs</var>; 
    <code>ucs-range->char-set</code> produces a fresh character set.

    <p>
    Note that ASCII codes are a subset of the Latin-1 codes, which are in turn
    a subset of the 16-bit Unicode codes, which are themselves a subset of the
    32-bit UCS-4 codes. We commit to a specific encoding in this routine,
    regardless of the underlying representation of characters, so that client
    code using this library will be portable. <em>I.e.</em>, a conformant Scheme
    implementation may use EBCDIC or SHIFT-JIS to encode characters; it must
    simply map the UCS characters from the given range into the native
    representation when possible, and report errors when not possible.

<!--
==== ->char-set
============================================================================-->
<dt class=proc-def>
<a name="->char-set"></a>
<code class=proc-def>->char-set</code><var> x -> char-set</var>
<dd class=proc-def>
    Coerces <var>x</var> into a char-set. 
    <var>X</var> may be a string, character or
    char-set. A string is converted to the set of its constituent characters;
    a character is converted to a singleton set; a char-set is returned
    as-is.
    This procedure is intended for use by other procedures that want to 
    provide "user-friendly," wide-spectrum interfaces to their clients.

</dl>

<!--========================================================================-->
<h2><a name="Querying">Querying character sets</a></h2>
<dl>

<!--
==== char-set-size
============================================================================-->
<dt class=proc-def>
<a name="char-set-size"></a>
<code class=proc-def>char-set-size</code><var> cs -> integer</var>
<dd class=proc-def>
    Returns the number of elements in character set <var>cs</var>.

<!--
==== char-set-count
============================================================================-->
<dt class=proc-def>
<a name="char-set-count"></a>
<code class=proc-def>char-set-count</code><var> pred cs -> integer</var>
<dd class=proc-def>
    Apply <var>pred</var> to the chars of character set <var>cs</var>, and return the number
    of chars that caused the predicate to return true.

<!--
==== char-set->list
============================================================================-->
<dt class=proc-def>
<a name="char-set->list"></a>
<code class=proc-def>char-set->list</code><var> cs -> character-list</var>
<dd class=proc-def>
    This procedure returns a list of the members of character set <var>cs</var>.
    The order in which <var>cs</var>'s characters appear in the list is not defined,
    and may be different from one call to another.

<!--
==== char-set->string
============================================================================-->
<dt class=proc-def>
<a name="char-set->string"></a>
<code class=proc-def>char-set->string</code><var> cs -> string</var>
<dd class=proc-def>
    This procedure returns a string containing the members of character set <var>cs</var>.
    The order in which <var>cs</var>'s characters appear in the string is not defined,
    and may be different from one call to another.

<!--
==== char-set-contains?
============================================================================-->
<dt class=proc-def>
<a name="char-set-contains-p"></a>
<code class=proc-def>char-set-contains?</code><var> cs char -> boolean</var>
<dd class=proc-def>
    This procedure tests <var>char</var> for membership in character set <var>cs</var>.

    <p>
    The MIT Scheme character-set package called this procedure
    <var>char-set-member?</var>, but the argument order isn't consistent with the name.

<!--
==== char-set-every char-set-any
============================================================================-->
<dt class=proc-def1>
<a name="char-set-every"></a>
<a name="char-set-any"></a>
<code class=proc-def>char-set-every</code><var> pred cs -> boolean</var>
<dt class=proc-defn><code class=proc-def>char-set-any&nbsp;&nbsp;</code><var> pred cs -> boolean</var>
<dd class=proc-def>
    The <code>char-set-every</code> procedure returns true if predicate <var>pred</var>
    returns true of every character in the character set <var>cs</var>.
    Likewise, <code>char-set-any</code> applies <var>pred</var> to every character in
    character set <var>cs</var>, and returns the first true value it finds.
    If no character produces a true value, it returns false.
    The order in which these procedures sequence through the elements of
    <var>cs</var> is not specified.

    <p>
    Note that if you need to determine the actual character on which a 
    predicate returns true, use <code>char-set-any</code> and arrange for the predicate 
    to return the character parameter as its true value, <em>e.g.</em>
<pre class=code-example>
(char-set-any (lambda (c) (and (char-upper-case? c) c)) 
              cs)
</pre>
</dl>

<!--========================================================================-->
<h2><a name="Algebra">Character-set algebra</a></h2>
<dl>

<!--
==== char-set-adjoin char-set-delete
============================================================================-->
<dt class=proc-def1>
<a name="char-set-adjoin"></a>
<a name="char-set-delete"></a>
<code class=proc-def>char-set-adjoin</code><var> cs char<sub>1</sub> ... -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-delete</code><var> cs char<sub>1</sub> ... -> char-set</var>
<dd class=proc-def>
    Add/delete the <var>char<sub>i</sub></var> characters to/from character set <var>cs</var>.

<!--
==== char-set-adjoin! char-set-delete!
============================================================================-->
<dt class=proc-def1>
<a name="char-set-adjoin!"></a>
<a name="char-set-delete!"></a>
<code class=proc-def>char-set-adjoin!</code><var> cs char<sub>1</sub> ... -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-delete!</code><var> cs char<sub>1</sub> ... -> char-set</var>
<dd class=proc-def>

    Linear-update variants. These procedures are allowed, but not
    required, to side-effect their first parameter.

<!--
==== char-set-complement char-set-union char-set-intersection 
==== char-set-difference char-set-xor char-set-diff+intersection
============================================================================-->
<dt class=proc-def1>
<a name="char-set-complement"></a>
<a name="char-set-union"></a>
<a name="char-set-intersection"></a>
<a name="char-set-difference"></a>
<a name="char-set-xor"></a>
<a name="char-set-diff+intersection"></a>
<code class=proc-def>char-set-complement</code><var> cs                     -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-union</code><var> cs<sub>1</sub> ...                 -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-intersection</code><var> cs<sub>1</sub> ...          -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-difference</code><var> cs<sub>1</sub> cs<sub>2</sub> ...        -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-xor</code><var> cs<sub>1</sub> ...                   -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-diff+intersection</code><var> cs<sub>1</sub> cs<sub>2</sub> ... -> [char-set char-set]</var>
<dd class=proc-def>
    These procedures implement set complement, union, intersection,
    difference, and exclusive-or for character sets. The union, intersection
    and xor operations are n-ary. The difference function is also n-ary,
    associates to the left (that is, it computes the difference between
    its first argument and the union of all the other arguments),
    and requires at least one argument.

    <p>
    Boundary cases:
<pre class=code-example>
(char-set-union) => char-set:empty
(char-set-intersection) => char-set:full
(char-set-xor) => char-set:empty
(char-set-difference <var>cs</var>) => <var>cs</var>
</pre>

    <p>
    <code>char-set-diff+intersection</code> returns both the difference and the
    intersection of the arguments -- it partitions its first parameter.
    It is equivalent to 
<pre class=code-example>
(values (char-set-difference <var>cs<sub>1</sub></var> <var>cs<sub>2</sub></var> ...)
        (char-set-intersection <var>cs<sub>1</sub></var> (char-set-union <var>cs<sub>2</sub></var> ...)))
</pre>
    but can be implemented more efficiently.

<p>
    Programmers should be aware that <code>char-set-complement</code> could potentially
    be a very expensive operation in Scheme implementations that provide
    a very large character type, such as 32-bit Unicode. If this is a
    possibility, sets can be complimented with respect to a smaller
    universe using <code>char-set-difference</code>.


<!--
==== char-set-complement! char-set-union! char-set-intersection! 
==== char-set-difference! char-set-xor! char-set-diff+intersection!
============================================================================-->
<dt class=proc-def1>
<a name="char-set-complement!"></a>
<a name="char-set-union!"></a>
<a name="char-set-intersection!"></a>
<a name="char-set-difference!"></a>
<a name="char-set-xor!"></a>
<a name="char-set-diff+intersection!"></a>
<code class=proc-def>char-set-complement!</code><var> cs                     -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-union!</code><var>  cs<sub>1</sub> cs<sub>2</sub> ...                   -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-intersection!</code><var>  cs<sub>1</sub> cs<sub>2</sub> ...          -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-difference!</code><var>  cs<sub>1</sub> cs<sub>2</sub> ...            -> char-set</var>
<dt class=proc-defi><code class=proc-def>char-set-xor!</code><var>  cs<sub>1</sub> cs<sub>2</sub> ...                   -> char-set</var>
<dt class=proc-defn><code class=proc-def>char-set-diff+intersection!</code><var>  cs<sub>1</sub> cs<sub>2</sub> cs<sub>3</sub> ... -> [char-set char-set]</var>
<dd class=proc-def>
    These are linear-update variants of the set-algebra functions.
    They are allowed, but not required, to side-effect their first (required)
    parameter.

    <p>
    <code>char-set-diff+intersection!</code> is allowed to side-effect both
    of its two required parameters, <var>cs<sub>1</sub></var>
    and <var>cs<sub>2</sub></var>.
</dl>

<!--========================================================================-->
<h2><a name="StandardCharsets">Standard character sets</a></h2>
<p>
Several character sets are predefined for convenience:
<a name="char-set:lower-case"></a>
<a name="char-set:lower-case"></a>
<a name="char-set:upper-case"></a>
<a name="char-set:title-case"></a>
<a name="char-set:letter"></a>
<a name="char-set:digit"></a>
<a name="char-set:letter+digit"></a>
<a name="char-set:graphic"></a>
<a name="char-set:printing"></a>
<a name="char-set:whitespace"></a>
<a name="char-set:iso-control"></a>
<a name="char-set:punctuation"></a>
<a name="char-set:symbol"></a>
<a name="char-set:hex-digit"></a>
<a name="char-set:blank"></a>
<a name="char-set:ascii"></a>
<a name="char-set:empty"></a>
<a name="char-set:full"></a>
<div class=inset>
<table cellpadding=0 cellspacing=0>
<tr><td><code>char-set:lower-case</code> </td><td>Lower-case letters</td></tr>
<tr><td><code>char-set:upper-case</code> </td><td>Upper-case letters</td></tr>
<tr><td><code>char-set:title-case</code> </td><td>Title-case letters</td></tr>
<tr><td><code>char-set:letter</code> </td><td>Letters</td></tr>
<tr><td><code>char-set:digit</code> </td><td>Digits</td></tr>
<tr><td><code>char-set:letter+digit</code> </td><td>Letters and digits</td></tr>
<tr><td><code>char-set:graphic</code> </td><td>Printing characters except spaces</td></tr>
<tr><td><code>char-set:printing</code> </td><td>Printing characters including spaces</td></tr>
<tr><td><code>char-set:whitespace</code> </td><td>Whitespace characters </td></tr>
<tr><td><code>char-set:iso-control</code> </td><td>The ISO control characters </td></tr>
<tr><td><code>char-set:punctuation</code> </td><td>Punctuation characters</td></tr>
<tr><td><code>char-set:symbol</code> </td><td>Symbol characters</td></tr>
<tr><td><code>char-set:hex-digit</code> </td><td>A hexadecimal digit: 0-9, A-F, a-f </td></tr>
<tr><td><code>char-set:blank</code> </td><td>Blank characters -- horizontal whitespace</td></tr>
<tr><td><code>char-set:ascii</code> </td><td>All characters in the ASCII set. </td></tr>
<tr><td><code>char-set:empty</code> </td><td>Empty set </td></tr>
<tr><td><code>char-set:full</code> </td><td>All characters </td></tr>
</table>
</div>

<p>
Note that there may be characters in <code>char-set:letter</code> that are neither upper or
lower case---this might occur in implementations that use a character type
richer than ASCII, such as Unicode. A "graphic character" is one that would
put ink on your page. While the exact composition of these sets may vary
depending upon the character type provided by the underlying Scheme system,
here are the definitions for some of the sets in an ASCII implementation:
<div class=inset>
<table cellpadding=0 cellspacing=0>
<tr><td><code>char-set:lower-case</code> </td><td>a-z </td></tr>
<tr><td><code>char-set:upper-case</code> </td><td>A-Z </td></tr>
<tr><td><code>char-set:letter</code> </td><td>A-Z and a-z </td></tr>
<tr><td><code>char-set:digit</code> </td><td>0123456789</td></tr>
<tr><td><code>char-set:punctuation</code> </td><td><code>!"#%&amp;'()*,-./:;?@[\]_{}</code></td></tr>
<tr><td><code>char-set:symbol</code> </td><td><code>$+&lt;=&gt;^`|~</code></td></tr>
<tr><td><code>char-set:whitespace</code> </td><td>Space, newline, tab, form feed, </td></tr>
<tr><td></td><td>                               vertical tab, carriage return </td></tr>
<tr><td><code>char-set:blank</code> </td><td>Space and tab </td></tr>
<tr><td><code>char-set:graphic</code> </td><td>letter + digit + punctuation + symbol</td></tr>
<tr><td><code>char-set:printing</code> </td><td>graphic + whitespace</td></tr>
<tr><td><code>char-set:iso-control</code> </td><td>ASCII 0-31 and 127 </td></tr>
</table>
</div>

<p>
Note that the existence of the <code>char-set:ascii</code> set implies that the underlying
character set is required to be at least as rich as ASCII (including
ASCII's control characters).

<p>
Rationale: The name choices reflect a shift from the older "alphabetic/numeric"
terms found in 
<abbr title="Revised^5 Report on Scheme"><a href="#R5RS">R5RS</a></abbr>
and Posix to newer, Unicode-influenced "letter/digit" lexemes.

<!--========================================================================-->
<h1><a name="StandardCharsetDefs">
    Unicode, Latin-1 and ASCII definitions of the standard character sets</a>
</h1>
<p>
In Unicode Scheme implementations, the base character sets are compatible with
Java's Unicode specifications. For ASCII or Latin-1, we simply restrict the
Unicode set specifications to their first 128 or 256 codes, respectively.
Scheme implementations that are not based on ASCII, Latin-1 or Unicode should
attempt to preserve the sense or spirit of these definitions.

<p>
The following descriptions frequently make reference to the "Unicode character
database." This is a file, available at URL
<div class=inset>
<a href="ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt">
ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt</a>
</div>
<p class=continue>
Each line contains a description of a Unicode character. The first
semicolon-delimited field of the line gives the hex value of the character's
code; the second field gives the name of the character, and the third field
gives a two-letter category. Other fields give simple 1-1 case-mappings for
the character and other information; see
<div class=inset>
<a href="ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.html">
ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.html</a>
</div>
<p class=continue>
for further description of the file's format. Note in particular the
two-letter category specified in the third field, which is referenced
frequently in the descriptions below.

<!--========================================================================-->
<h2><a name="lower-case-def">char-set:lower-case</a></h2>
<p>
For Unicode, we follow Java's specification: a character is lowercase if
<ul>
<li> it is not in the range [U+2000,U+2FFF], and
<li> the Unicode attribute table does not give a lowercase mapping for it, and
<li> at least one of the following is true:
  <ul>
  <li> the Unicode attribute table gives a mapping to uppercase 
    for the character, or
  <li> the name for the character in the Unicode attribute table contains
    the words "SMALL LETTER" or "SMALL LIGATURE".
  </ul>
</ul>

<p>
The lower-case ASCII characters are 
<div class=inset>
    abcdefghijklmnopqrstuvwxyz
</div>
<p class=continue>
Latin-1 adds another 33 lower-case characters to the ASCII set:
<div class=inset>
<table cellpadding=0 cellspacing=0>
<tr><td>00B5</td> <td>MICRO SIGN</td></tr>
<tr><td>00DF</td> <td>LATIN SMALL LETTER SHARP S</td></tr>
<tr><td>00E0</td> <td>LATIN SMALL LETTER A WITH GRAVE</td></tr>
<tr><td>00E1</td> <td>LATIN SMALL LETTER A WITH ACUTE</td></tr>
<tr><td>00E2</td> <td>LATIN SMALL LETTER A WITH CIRCUMFLEX</td></tr>
<tr><td>00E3</td> <td>LATIN SMALL LETTER A WITH TILDE</td></tr>
<tr><td>00E4</td> <td>LATIN SMALL LETTER A WITH DIAERESIS</td></tr>
<tr><td>00E5</td> <td>LATIN SMALL LETTER A WITH RING ABOVE</td></tr>
<tr><td>00E6</td> <td>LATIN SMALL LETTER AE</td></tr>
<tr><td>00E7</td> <td>LATIN SMALL LETTER C WITH CEDILLA</td></tr>
<tr><td>00E8</td> <td>LATIN SMALL LETTER E WITH GRAVE</td></tr>
<tr><td>00E9</td> <td>LATIN SMALL LETTER E WITH ACUTE</td></tr>
<tr><td>00EA</td> <td>LATIN SMALL LETTER E WITH CIRCUMFLEX</td></tr>
<tr><td>00EB</td> <td>LATIN SMALL LETTER E WITH DIAERESIS</td></tr>
<tr><td>00EC</td> <td>LATIN SMALL LETTER I WITH GRAVE</td></tr>
<tr><td>00ED</td> <td>LATIN SMALL LETTER I WITH ACUTE</td></tr>
<tr><td>00EE</td> <td>LATIN SMALL LETTER I WITH CIRCUMFLEX</td></tr>
<tr><td>00EF</td> <td>LATIN SMALL LETTER I WITH DIAERESIS</td></tr>
<tr><td>00F0</td> <td>LATIN SMALL LETTER ETH</td></tr>
<tr><td>00F1</td> <td>LATIN SMALL LETTER N WITH TILDE</td></tr>
<tr><td>00F2</td> <td>LATIN SMALL LETTER O WITH GRAVE</td></tr>
<tr><td>00F3</td> <td>LATIN SMALL LETTER O WITH ACUTE</td></tr>
<tr><td>00F4</td> <td>LATIN SMALL LETTER O WITH CIRCUMFLEX</td></tr>
<tr><td>00F5</td> <td>LATIN SMALL LETTER O WITH TILDE</td></tr>
<tr><td>00F6</td> <td>LATIN SMALL LETTER O WITH DIAERESIS</td></tr>
<tr><td>00F8</td> <td>LATIN SMALL LETTER O WITH STROKE</td></tr>
<tr><td>00F9</td> <td>LATIN SMALL LETTER U WITH GRAVE</td></tr>
<tr><td>00FA</td> <td>LATIN SMALL LETTER U WITH ACUTE</td></tr>
<tr><td>00FB</td> <td>LATIN SMALL LETTER U WITH CIRCUMFLEX</td></tr>
<tr><td>00FC</td> <td>LATIN SMALL LETTER U WITH DIAERESIS</td></tr>
<tr><td>00FD</td> <td>LATIN SMALL LETTER Y WITH ACUTE</td></tr>
<tr><td>00FE</td> <td>LATIN SMALL LETTER THORN</td></tr>
<tr><td>00FF</td> <td>LATIN SMALL LETTER Y WITH DIAERESIS</td></tr>
</table>
</div>
<p class=continue>
Note that three of these have no corresponding Latin-1 upper-case character:
<div class=inset>
<table cellpadding=0 cellspacing=0>
<tr><td>00B5</td> <td>MICRO SIGN</td></tr>
<tr><td>00DF</td> <td>LATIN SMALL LETTER SHARP S</td></tr>
<tr><td>00FF</td> <td>LATIN SMALL LETTER Y WITH DIAERESIS</td></tr>
</table>
</div>
<p class=continue>
(The compatibility micro character uppercases to the non-Latin-1 Greek capital
mu; the German sharp s character uppercases to the pair of characters "SS,"
and the capital y-with-diaeresis is non-Latin-1.)

<p>
(Note that the Java spec for lowercase characters given at
<div class=inset>
<a href="http://java.sun.com/docs/books/jls/html/javalang.doc4.html#14345">
http://java.sun.com/docs/books/jls/html/javalang.doc4.html#14345</a>
</div>
<p class=continue>
is inconsistent. U+00B5 MICRO SIGN fulfills the requirements for a lower-case
character (as of Unicode 3.0), but is not given in the numeric list of
lower-case character codes.)

<p>
(Note that the Java spec for <code>isLowerCase()</code> given at
<div class=inset>
<a href="http://java.sun.com/products/jdk/1.2/docs/api/java/lang/Character.html#isLowerCase(char)">
http://java.sun.com/products/jdk/1.2/docs/api/java/lang/Character.html#isLowerCase(char)</a>
</div>
<p class=continue>
gives three mutually inconsistent definitions of "lower case." The first is
the definition used in this SRFI. Following text says "A character is
considered to be lowercase if and only if it is specified to be lowercase by
the Unicode 2.0 standard (category Ll in the Unicode specification data
file)." The former spec excludes U+00AA FEMININE ORDINAL INDICATOR and
U+00BA MASCULINE ORDINAL INDICATOR; the later spec includes them. Finally,
the spec enumerates a list of characters in the Latin-1 subset; this list
excludes U+00B5 MICRO SIGN, which is included in both of the previous specs.) 

<!--========================================================================-->
<h2><a name="upper-case-def">char-set:upper-case</a></h2>
<p>
For Unicode, we follow Java's specification: a character is uppercase if
<ul>
<li> it is not in the range [U+2000,U+2FFF], and
<li> the Unicode attribute table does not give an uppercase mapping for it
(this excludes titlecase characters), and
<li> at least one of the following is true:
  <ul>
  <li> the Unicode attribute table gives a mapping to lowercase 
    for the character, or
  <li> the name for the character in the Unicode attribute table contains
    the words "CAPITAL LETTER" or "CAPITAL LIGATURE".
  </ul>
</ul>

<p>
The upper-case ASCII characters are 
<div class=inset>
ABCDEFGHIJKLMNOPQRSTUVWXYZ
</div>
<p class=continue>
Latin-1 adds another 30 upper-case characters to the ASCII set:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>00C0</td> <td>LATIN CAPITAL LETTER A WITH GRAVE</td></tr>
<tr><td>00C1</td> <td>LATIN CAPITAL LETTER A WITH ACUTE</td></tr>
<tr><td>00C2</td> <td>LATIN CAPITAL LETTER A WITH CIRCUMFLEX</td></tr>
<tr><td>00C3</td> <td>LATIN CAPITAL LETTER A WITH TILDE</td></tr>
<tr><td>00C4</td> <td>LATIN CAPITAL LETTER A WITH DIAERESIS</td></tr>
<tr><td>00C5</td> <td>LATIN CAPITAL LETTER A WITH RING ABOVE</td></tr>
<tr><td>00C6</td> <td>LATIN CAPITAL LETTER AE</td></tr>
<tr><td>00C7</td> <td>LATIN CAPITAL LETTER C WITH CEDILLA</td></tr>
<tr><td>00C8</td> <td>LATIN CAPITAL LETTER E WITH GRAVE</td></tr>
<tr><td>00C9</td> <td>LATIN CAPITAL LETTER E WITH ACUTE</td></tr>
<tr><td>00CA</td> <td>LATIN CAPITAL LETTER E WITH CIRCUMFLEX</td></tr>
<tr><td>00CB</td> <td>LATIN CAPITAL LETTER E WITH DIAERESIS</td></tr>
<tr><td>00CC</td> <td>LATIN CAPITAL LETTER I WITH GRAVE</td></tr>
<tr><td>00CD</td> <td>LATIN CAPITAL LETTER I WITH ACUTE</td></tr>
<tr><td>00CE</td> <td>LATIN CAPITAL LETTER I WITH CIRCUMFLEX</td></tr>
<tr><td>00CF</td> <td>LATIN CAPITAL LETTER I WITH DIAERESIS</td></tr>
<tr><td>00D0</td> <td>LATIN CAPITAL LETTER ETH</td></tr>
<tr><td>00D1</td> <td>LATIN CAPITAL LETTER N WITH TILDE</td></tr>
<tr><td>00D2</td> <td>LATIN CAPITAL LETTER O WITH GRAVE</td></tr>
<tr><td>00D3</td> <td>LATIN CAPITAL LETTER O WITH ACUTE</td></tr>
<tr><td>00D4</td> <td>LATIN CAPITAL LETTER O WITH CIRCUMFLEX</td></tr>
<tr><td>00D5</td> <td>LATIN CAPITAL LETTER O WITH TILDE</td></tr>
<tr><td>00D6</td> <td>LATIN CAPITAL LETTER O WITH DIAERESIS</td></tr>
<tr><td>00D8</td> <td>LATIN CAPITAL LETTER O WITH STROKE</td></tr>
<tr><td>00D9</td> <td>LATIN CAPITAL LETTER U WITH GRAVE</td></tr>
<tr><td>00DA</td> <td>LATIN CAPITAL LETTER U WITH ACUTE</td></tr>
<tr><td>00DB</td> <td>LATIN CAPITAL LETTER U WITH CIRCUMFLEX</td></tr>
<tr><td>00DC</td> <td>LATIN CAPITAL LETTER U WITH DIAERESIS</td></tr>
<tr><td>00DD</td> <td>LATIN CAPITAL LETTER Y WITH ACUTE</td></tr>
<tr><td>00DE</td> <td>LATIN CAPITAL LETTER THORN</td></tr>
</table>
</div>
<!--========================================================================-->
<h2><a name="title-case-def">char-set:title-case</a></h2>
<p>
In Unicode, a character is titlecase if it has the category Lt in
the character attribute database. There are very few of these characters;
here is the entire 31-character list as of Unicode 3.0:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>01C5 </td><td nowrap> LATIN CAPITAL LETTER D WITH SMALL LETTER Z WITH CARON
</td></tr>
<tr><td>01C8 </td><td nowrap> LATIN CAPITAL LETTER L WITH SMALL LETTER J
</td></tr>
<tr><td>01CB </td><td nowrap> LATIN CAPITAL LETTER N WITH SMALL LETTER J
</td></tr>
<tr><td>01F2 </td><td nowrap> LATIN CAPITAL LETTER D WITH SMALL LETTER Z
</td></tr>
<tr><td>1F88 </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH PSILI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F89 </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH DASIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8A </td><td nowrap>GREEK CAPITAL LETTER ALPHA WITH PSILI AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8B </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH DASIA AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8C </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH PSILI AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8D </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH DASIA AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8E </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH PSILI AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F8F </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH DASIA AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F98 </td><td nowrap> GREEK CAPITAL LETTER ETA WITH PSILI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F99 </td><td nowrap> GREEK CAPITAL LETTER ETA WITH DASIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9A </td><td nowrap> GREEK CAPITAL LETTER ETA WITH PSILI AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9B </td><td nowrap> GREEK CAPITAL LETTER ETA WITH DASIA AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9C </td><td nowrap> GREEK CAPITAL LETTER ETA WITH PSILI AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9D </td><td nowrap> GREEK CAPITAL LETTER ETA WITH DASIA AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9E </td><td nowrap> GREEK CAPITAL LETTER ETA WITH PSILI AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1F9F </td><td nowrap> GREEK CAPITAL LETTER ETA WITH DASIA AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FA8 </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH PSILI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FA9 </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH DASIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAA </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH PSILI AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAB </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH DASIA AND VARIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAC </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH PSILI AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAD </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH DASIA AND OXIA AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAE </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH PSILI AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FAF </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH DASIA AND PERISPOMENI AND PROSGEGRAMMENI
</td></tr>
<tr><td>1FBC </td><td nowrap> GREEK CAPITAL LETTER ALPHA WITH PROSGEGRAMMENI
</td></tr>
<tr><td>1FCC </td><td nowrap> GREEK CAPITAL LETTER ETA WITH PROSGEGRAMMENI
</td></tr>
<tr><td>1FFC </td><td nowrap> GREEK CAPITAL LETTER OMEGA WITH PROSGEGRAMMENI
</td></tr>
</table>
</div>
<p>
There are no ASCII or Latin-1 titlecase characters.


<!--========================================================================-->
<h2><a name="letter-def">char-set:letter</a></h2>
<p>
In Unicode, a letter is any character with one of the letter categories
(Lu, Ll, Lt, Lm, Lo) in the Unicode character database. 

<p>
There are 52 ASCII letters
<div class=indent>
    abcdefghijklmnopqrstuvwxyz <br>
    ABCDEFGHIJKLMNOPQRSTUVWXYZ <br>
</div>
<p>
There are 117 Latin-1 letters. These are the 115 characters that are
members of the Latin-1 <code>char-set:lower-case</code> and <code>char-set:upper-case</code> sets, 
plus
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>00AA</td> <td>FEMININE ORDINAL INDICATOR</td></tr>
<tr><td>00BA</td> <td>MASCULINE ORDINAL INDICATOR</td></tr>
</table>
</div>
<p class=continue>
(These two letters are considered lower-case by Unicode, but not by
Java or SRFI 14.)

<!--========================================================================-->
<h2><a name="digit-def">char-set:digit</a></h2>

<p>
In Unicode, a character is a digit if it has the category Nd in
the character attribute database. In Latin-1 and ASCII, the only
such characters are 0123456789. In Unicode, there are other digit
characters in other code blocks, such as Gujarati digits and Tibetan
digits.


<!--========================================================================-->
<h2><a name="hex-digit-def">char-set:hex-digit</a></h2>
<p>
The only hex digits are 0123456789abcdefABCDEF.


<!--========================================================================-->
<h2><a name="letter+digit-def">char-set:letter+digit</a></h2>
<p>
The union of <code>char-set:letter</code> and <code>char-set:digit.</code>

<!--========================================================================-->
<h2><a name="graphic-def">char-set:graphic</a></h2>
<p>
A graphic character is one that would put ink on paper. The ASCII and Latin-1
graphic characters are the members of
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td><code>char-set:letter</code></td></tr>
<tr><td><code>char-set:digit</code></td></tr>
<tr><td><code>char-set:punctuation</code></td></tr>
<tr><td><code>char-set:symbol</code></td></tr>
</table>
</div>

<!--========================================================================-->
<h2><a name="printing-def">char-set:printing</a></h2>
<p>
A printing character is one that would occupy space when printed, <em>i.e.</em>,
a graphic character or a space character. <code>char-set:printing</code> is the union
of <code>char-set:whitespace</code> and <code>char-set:graphic.</code>

<!--========================================================================-->
<h2><a name="whitespace-def">char-set:whitespace</a></h2>
<p>
In Unicode, a whitespace character is either
<ul>
  <li> a character with one of the space, line, or paragraph separator categories
    (Zs, Zl or Zp) of the Unicode character database.
  <li> U+0009 Horizontal tabulation (\t control-I)
  <li> U+000A Line feed (\n control-J)
  <li> U+000B Vertical tabulation (\v control-K)
  <li> U+000C Form feed (\f control-L)
  <li> U+000D Carriage return (\r control-M)
</ul>

<p>
There are 24 whitespace characters in Unicode 3.0:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>0009</td> <td>HORIZONTAL TABULATION </td> <td>  \t control-I</td></tr>
<tr><td>000A</td> <td>LINE FEED         </td> <td> \n control-J</td></tr>
<tr><td>000B</td> <td>VERTICAL TABULATION       </td> <td> \v control-K</td></tr>
<tr><td>000C</td> <td>FORM FEED         </td> <td> \f control-L</td></tr>
<tr><td>000D</td> <td>CARRIAGE RETURN   </td> <td> \r control-M</td></tr>
<tr><td>0020</td> <td>SPACE                     </td> <td> Zs</td></tr>
<tr><td>00A0</td> <td>NO-BREAK SPACE    </td> <td> Zs</td></tr>
<tr><td>1680</td> <td>OGHAM SPACE MARK  </td> <td> Zs</td></tr>
<tr><td>2000</td> <td>EN QUAD           </td> <td> Zs</td></tr>
<tr><td>2001</td> <td>EM QUAD           </td> <td> Zs</td></tr>
<tr><td>2002</td> <td>EN SPACE          </td> <td> Zs</td></tr>
<tr><td>2003</td> <td>EM SPACE          </td> <td> Zs</td></tr>
<tr><td>2004</td> <td>THREE-PER-EM SPACE        </td> <td> Zs</td></tr>
<tr><td>2005</td> <td>FOUR-PER-EM SPACE </td> <td> Zs</td></tr>
<tr><td>2006</td> <td>SIX-PER-EM SPACE  </td> <td> Zs</td></tr>
<tr><td>2007</td> <td>FIGURE SPACE              </td> <td> Zs</td></tr>
<tr><td>2008</td> <td>PUNCTUATION SPACE </td> <td> Zs</td></tr>
<tr><td>2009</td> <td>THIN SPACE                </td> <td> Zs</td></tr>
<tr><td>200A</td> <td>HAIR SPACE                </td> <td> Zs</td></tr>
<tr><td>200B</td> <td>ZERO WIDTH SPACE  </td> <td> Zs</td></tr>
<tr><td>2028</td> <td>LINE SEPARATOR    </td> <td> Zl</td></tr>
<tr><td>2029</td> <td>PARAGRAPH SEPARATOR       </td> <td> Zp</td></tr>
<tr><td>202F</td> <td>NARROW NO-BREAK SPACE     </td> <td> Zs</td></tr>
<tr><td>3000</td> <td>IDEOGRAPHIC SPACE </td> <td> Zs</td></tr>
</table>
</div>
<p>
The ASCII whitespace characters are the first six characters in the above list
-- line feed, horizontal tabulation, vertical tabulation, form feed, carriage
return, and space. These are also exactly the characters recognised by the
Posix <code>isspace()</code> procedure. Latin-1 adds the no-break space.

<p>
Note: Java's <code>isWhitespace()</code> method is incompatible, including
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>0009</td> <td>HORIZONTAL TABULATION </td> <td>  (\t control-I)</td></tr>
<tr><td>001C</td> <td>FILE SEPARATOR   </td> <td> (control-\)</td></tr>
<tr><td>001D</td> <td>GROUP SEPARATOR  </td> <td>(control-])</td></tr>
<tr><td>001E</td> <td>RECORD SEPARATOR </td> <td>(control-^)</td></tr>
<tr><td>001F</td> <td>UNIT SEPARATOR   </td> <td>(control-_)</td></tr>
</table>
</div>
<p class=continue>
and excluding
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>00A0</td> <td>NO-BREAK SPACE</td></tr>
</table>
</div>
<p>
Java's excluding the no-break space means that tokenizers can simply break
character streams at "whitespace" boundaries. However, the exclusion introduces
exceptions in other places, <em>e.g.</em> <code>char-set:printing</code> is no longer simply the
union of <code>char-set:graphic</code> and <code>char-set:whitespace.</code>


<!--========================================================================-->
<h2><a name="iso-control-def">char-set:iso-control</a></h2>
<p>
The ISO control characters are the Unicode/Latin-1 characters in the ranges
[U+0000,U+001F] and [U+007F,U+009F].

<p>
ASCII restricts this set to the characters in the range [U+0000,U+001F] 
plus the character U+007F.

<p>
Note that Unicode defines other control characters which do not belong to this
set (hence the qualifying prefix "iso-" in the name). This restriction is
compatible with the Java <code>IsISOControl()</code> method.


<!--========================================================================-->
<h2><a name="punctuation-def">char-set:punctuation</a></h2>
<p>
In Unicode, a punctuation character is any character that has one of the
punctuation categories in the Unicode character database (Pc, Pd, Ps,
Pe, Pi, Pf, or Po.)

<p>
ASCII has 23 punctuation characters:
<pre class=code-example>
!"#%&amp;'()*,-./:;?@[\]_{}
</pre>
<p>
Latin-1 adds six more:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>00A1 </td> <td> INVERTED EXCLAMATION MARK
<tr><td>00AB </td> <td> LEFT-POINTING DOUBLE ANGLE QUOTATION MARK
<tr><td>00AD </td> <td> SOFT HYPHEN
<tr><td>00B7 </td> <td> MIDDLE DOT
<tr><td>00BB </td> <td> RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK
<tr><td>00BF </td> <td> INVERTED QUESTION MARK
</table>
</div>

<p>
Note that the nine ASCII characters <code>$+<=>^`|~</code> are <em>not</em>
punctuation. They are "symbols."


<!--========================================================================-->
<h2><a name="symbol-def">char-set:symbol</a></h2>
<p>
In Unicode, a symbol is any character that has one of the symbol categories
in the Unicode character database (Sm, Sc, Sk, or So). There
are nine ASCII symbol characters:
<pre class=code-example>
$+&lt;=&gt;^`|~
</pre>
<p>
Latin-1 adds 18 more:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>00A2 </td> <td> CENT SIGN </td></tr>
<tr><td>00A3 </td> <td> POUND SIGN </td></tr>
<tr><td>00A4 </td> <td> CURRENCY SIGN </td></tr>
<tr><td>00A5 </td> <td> YEN SIGN </td></tr>
<tr><td>00A6 </td> <td> BROKEN BAR </td></tr>
<tr><td>00A7 </td> <td> SECTION SIGN </td></tr>
<tr><td>00A8 </td> <td> DIAERESIS </td></tr>
<tr><td>00A9 </td> <td> COPYRIGHT SIGN </td></tr>
<tr><td>00AC </td> <td> NOT SIGN </td></tr>
<tr><td>00AE </td> <td> REGISTERED SIGN </td></tr>
<tr><td>00AF </td> <td> MACRON </td></tr>
<tr><td>00B0 </td> <td> DEGREE SIGN </td></tr>
<tr><td>00B1 </td> <td> PLUS-MINUS SIGN </td></tr>
<tr><td>00B4 </td> <td> ACUTE ACCENT </td></tr>
<tr><td>00B6 </td> <td> PILCROW SIGN </td></tr>
<tr><td>00B8 </td> <td> CEDILLA </td></tr>
<tr><td>00D7 </td> <td> MULTIPLICATION SIGN </td></tr>
<tr><td>00F7 </td> <td> DIVISION SIGN </td></tr>
</table>
</div>

<!--========================================================================-->
<h2><a name="blank-def">char-set:blank</a></h2>

<p>
Blank chars are horizontal whitespace. In Unicode, a blank character is either
<ul>
  <li> a character with the space separator category (Zs) in the Unicode 
    character database.
  <li> U+0009 Horizontal tabulation (\t control-I)
</ul>

<p>
There are eighteen blank characters in Unicode 3.0:
<div class=inset>
<table cellspacing=0 cellpadding=0>
<tr><td>0009 </td> <td> HORIZONTAL TABULATION   </td> <td> \t control-I </td></tr>
<tr><td>0020 </td> <td> SPACE                   </td> <td> Zs </td></tr>
<tr><td>00A0 </td> <td> NO-BREAK SPACE  </td> <td> Zs </td></tr>
<tr><td>1680 </td> <td> OGHAM SPACE MARK        </td> <td> Zs </td></tr>
<tr><td>2000 </td> <td> EN QUAD         </td> <td> Zs </td></tr>
<tr><td>2001 </td> <td> EM QUAD         </td> <td> Zs </td></tr>
<tr><td>2002 </td> <td> EN SPACE                </td> <td> Zs </td></tr>
<tr><td>2003 </td> <td> EM SPACE                </td> <td> Zs </td></tr>
<tr><td>2004 </td> <td> THREE-PER-EM SPACE      </td> <td> Zs </td></tr>
<tr><td>2005 </td> <td> FOUR-PER-EM SPACE       </td> <td> Zs </td></tr>
<tr><td>2006 </td> <td> SIX-PER-EM SPACE        </td> <td> Zs </td></tr>
<tr><td>2007 </td> <td> FIGURE SPACE            </td> <td> Zs </td></tr>
<tr><td>2008 </td> <td> PUNCTUATION SPACE       </td> <td> Zs </td></tr>
<tr><td>2009 </td> <td> THIN SPACE              </td> <td> Zs </td></tr>
<tr><td>200A </td> <td> HAIR SPACE              </td> <td> Zs </td></tr>
<tr><td>200B </td> <td> ZERO WIDTH SPACE        </td> <td> Zs </td></tr>
<tr><td>202F </td> <td> NARROW NO-BREAK SPACE   </td> <td> Zs </td></tr>
<tr><td>3000 </td> <td> IDEOGRAPHIC SPACE       </td> <td> Zs </td></tr>
</table>
</div>
<p>
The ASCII blank characters are the first two characters above --
horizontal tab and space. Latin-1 adds the no-break space.

<p>
Java doesn't have the concept of "blank" characters, so there are no
compatibility issues.


<!--========================================================================-->
<h1><a name="ReferenceImp">Reference implementation</a></h1>
<p>
This SRFI comes with a reference implementation. It resides at:
<div class=inset>
    <a href="http://srfi.schemers.org/srfi-14/srfi-14.scm">
http://srfi.schemers.org/srfi-14/srfi-14.scm</a>
</div>
<p class=continue>
I have placed this source on the Net with an unencumbered, "open" copyright.
Some of the code in the reference implementation bears a distant family
relation to the MIT Scheme implementation, and being derived from that code,
is covered by the MIT Scheme copyright (which is a generic BSD-style
open-source copyright -- see the source file for details). The remainder of
the code was written by myself for scsh or for this SRFI; I have placed this
code under the scsh copyright, which is also a generic BSD-style open-source
copyright.

<p>
The code is written for portability and should be simple to port to
any Scheme. It has only the following deviations from R4RS, clearly
discussed in the comments:
<ul>
  <li> an <code>error</code> procedure;
  <li> the R5RS <code>values</code> procedure for producing multiple return values;
  <li> a simple <code>check-arg</code> procedure for argument checking;
  <li> <code>let-optionals*</code> and <code>:optional</code> macros for for parsing, checking and defaulting
    optional arguments from rest lists;
  <li> The SRFI-19 <code>define-record-type</code> form;
  <li> <code>bitwise-and</code> for the hash function;
  <li> <code>%latin1->char</code> and <code>%char->latin1</code>.
</ul>

<p>
The library is written for clarity and well-commented; the current source is
about 375 lines of source code and 375 lines of comments and white space.
It is also written for efficiency. Fast paths are provided for common cases.

<p>
This is not to say that the implementation can't be tuned up for
a specific Scheme implementation. There are notes in comments addressing
ways implementors can tune the reference implementation for performance.

<p>
In short, I've written the reference implementation to make it as painless
as possible for an implementor -- or a regular programmer -- to adopt this
library and get good results with it.

<p>
The code uses a rather simple-minded, inefficient representation for
ASCII/Latin-1 char-sets -- a 256-character string. The character whose code is
<var>i</var> is in the set if <var>s[i]</var> = ASCII 1 (soh, or ^a); 
not in the set if <var>s[i]</var> = ASCII 0 (nul). 
A much faster and denser representation would be 16 or 32 bytes worth
of bit string. A portable implementation using bit sets awaits standards for
bitwise logical-ops and byte vectors.

<p>
"Large" character types, such as Unicode, should use a sparse representation,
taking care that the Latin-1 subset continues to be represented with a
dense 32-byte bit set.


<!--========================================================================-->
<h1><a name="Acknowledgements">Acknowledgements</a></h1>
<p>
The design of this library benefited greatly from the feedback provided during
the SRFI discussion phase. Among those contributing thoughtful commentary and
suggestions, both on the mailing list and by private discussion, were Paolo
Amoroso, Lars Arvestad, Alan Bawden, Jim Bender, Dan Bornstein, Per Bothner,
Will Clinger, Brian Denheyer, Kent Dybvig, Sergei Egorov, Marc Feeley,
Matthias Felleisen, Will Fitzgerald, Matthew Flatt, Arthur A. Gleckler, Ben
Goetter, Sven Hartrumpf, Erik Hilsdale, Shiro Kawai, Richard Kelsey, Oleg
Kiselyov, Bengt Kleberg, Donovan Kolbly, Bruce Korb, Shriram Krishnamurthi,
Bruce Lewis, Tom Lord, Brad Lucier, Dave Mason, David Rush, Klaus Schilling,
Jonathan Sobel, Mike Sperber, Mikael Staldal, Vladimir Tsyshevsky, Donald
Welsh, and Mike Wilson. I am grateful to them for their assistance.

<p>
I am also grateful the authors, implementors and documentors of all the
systems mentioned in the introduction. Aubrey Jaffer should be noted for his
work in producing Web-accessible versions of the R5RS spec, which was a
tremendous aid.

<p>
This is not to imply that these individuals necessarily endorse the final
results, of course. 

<p>
During this document's long development period, great patience was exhibited
by Mike Sperber, who is the editor for the SRFI, and by Hillary Sullivan,
who is not.

<!--========================================================================-->
<h1><a name="Links">References &amp; links</a></h1>

<dl>
<dt class=biblio><strong><a name="Java">[Java]</a></strong>
<dd>
    The following URLs provide documentation on relevant Java classes. <br>

    <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/lang/Character.html">http://java.sun.com/products/jdk/1.2/docs/api/java/lang/Character.html</a>
    <br>
    <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/lang/String.html">http://java.sun.com/products/jdk/1.2/docs/api/java/lang/String.html</a>
    <br>
    <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/lang/StringBuffer.html">http://java.sun.com/products/jdk/1.2/docs/api/java/lang/StringBuffer.html</a>
    <br>
    <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/text/Collator.html">http://java.sun.com/products/jdk/1.2/docs/api/java/text/Collator.html</a>
    <br>
    <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/text/package-summary.html">http://java.sun.com/products/jdk/1.2/docs/api/java/text/package-summary.html</a>

<dt class=biblio><strong><a name="MIT-Scheme">[MIT-Scheme]</a></strong>
<dd>
    <a href="http://www.swiss.ai.mit.edu/projects/scheme/">http://www.swiss.ai.mit.edu/projects/scheme/</a>

<dt class=biblio><strong><a name="R5RS">[R5RS]</a></strong></dt>
<dd>Revised<sup>5</sup> report on the algorithmic language Scheme.<br>
    R. Kelsey, W. Clinger, J. Rees (editors). <br>
    Higher-Order and Symbolic Computation, Vol. 11, No. 1, September, 1998. <br>
    and ACM SIGPLAN Notices, Vol. 33, No. 9, October, 1998. <br>
    Available at <a href="http://www.schemers.org/Documents/Standards/">
    http://www.schemers.org/Documents/Standards/</a>.

<dt class=biblio><strong>[SRFI]</strong></dt>
<dd>
    The SRFI web site. <br>
    <a href="http://srfi.schemers.org/">http://srfi.schemers.org/</a>

<dt class=biblio><strong>[SRFI-14]</strong></dt>
<dd>
    SRFI-14: String libraries. <br>
    <a href="http://srfi.schemers.org/srfi-14/">http://srfi.schemers.org/srfi-14/</a>

    <dl>    
    <dt>
      This document, in HTML:
    <dd><a href="http://srfi.schemers.org/srfi-14/srfi-14.html">
        http://srfi.schemers.org/srfi-14/srfi-14.html</a>

    <dt>
      This document, in plain text format:
    <dd><a href="http://srfi.schemers.org/srfi-14/srfi-14.txt">
        http://srfi.schemers.org/srfi-14/srfi-14.txt</a>

    <dt> Source code for the reference implementation:
    <dd>
      <a href="http://srfi.schemers.org/srfi-14/srfi-14.scm">
         http://srfi.schemers.org/srfi-14/srfi-14.scm</a>

    <dt> Scheme 48 module specification, with typings:
    <dd>
      <a href="http://srfi.schemers.org/srfi-14/srfi-14-s48-module.scm">
        http://srfi.schemers.org/srfi-14/srfi-14-s48-module.scm</a>

    <dt> Regression-test suite:
    <dd> <a href="http://srfi.schemers.org/srfi-14/srfi-14-tests.scm">
         http://srfi.schemers.org/srfi-14/srfi-14-tests.scm</a>

    </dl>
</dd>

<dt class=biblio><strong><a name="Unicode">[Unicode]</a></strong>
<dd>
    <a href="http://www.unicode.org/">http://www.unicode.org/</a>

<dt class=biblio><strong><a name="UnicodeData">[UnicodeData]</a></strong>
<dd>
    The Unicode character database. <br>
    <a href="ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt">ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt</a>
    <br>
    <a href="ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.html">ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.html</a>
</dl>

<!--========================================================================-->
<h1><a name="Copyright">Copyright</a></h1>

<p>
Certain portions of this document -- the specific, marked segments of text
describing the <abbr title="Revised^5 Report on Scheme"><a href="#R5RS">R5RS</a></abbr> procedures -- were adapted with permission from the R5RS
report.
    
<p>
All other text is copyright (C) Olin Shivers (1998, 1999, 2000). 
All Rights Reserved. 

<p>
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
</p>
<p>
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
</p>
<p>
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
</p>

</body>
</html>
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